*** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.ccp4.ac.uk ***
> Ethan Merritt wrote: > I was asked off-list if the failure to replace scattering > factors in atomsf.lib could also explain negative electron > density at Se sites in maps made for SeMet proteins. > The short answer is "yes, but..." > The longer answer continues... <long answer removed> Following this logic (for general anomalous stuff, not necessarily Se), shouldn't this be done for all atoms, not just the anomalous sites? Unfortunately, I could argue this both ways (which is a sure sign I'm confused): For - numerous small changes in f' from non-anomalous atoms will add up for larger structures; and even for smaller structures it's probably better if the model is as accurate a description as possible of the data (and would probably improve the statistics). Against - probably no way to measure f' of the non-anomalous atoms (unless there's some way to de-convolute the fluroescence scan, which is dominated by the anomalous atoms), so you'd have to use calculated values; f' is not resolution-dependent, so errors here can be absorbed by the scale factor (however, this is somewhat of a fudge factor, seeing as it's unlikely that the variation in f' for all atom types is uniform). Is this something that people generally worry about during refinement? Pete Pete Meyer Fu Lab BMCB grad student Cornell University
